Observation of the Resonant Character of the Z(4430)[superscript −] State

Abstract

Resonant structures in B[superscript 0] → ψ[superscript ′]π[superscript −]K[superscript +] decays are analyzed by performing a four-dimensional fit of the decay amplitude, using pp collision data corresponding to 3 fb[superscript −1] collected with the LHCb detector. The data cannot be described with K[superscript +]π[superscript −] resonances alone, which is confirmed with a model-independent approach. A highly significant Z(4430)[superscript −] → ψ[superscript ′]π[superscript −] component is required, thus confirming the existence of this state. The observed evolution of the Z(4430)[superscript −] amplitude with the ψ[superscript ′]π[superscript −] mass establishes the resonant nature of this particle. The mass and width measurements are substantially improved. The spin parity is determined unambiguously to be 1[superscript +].